Topeka ? Voters in Kansas will have to show photo identification to cast ballots under a law signed Monday by Gov. Sam Brownback, who predicted that the new requirement won’t cause obstacles at the polls.

Brownback and many fellow Republicans see the measure as an important check on potential election fraud, but a state leader of the National Association for the Advancement of Colored People called the change “radical” and one that could leave some voters disenfranchised.

Brownback signed the legislation at a ceremony at the Statehouse with Secretary of State Kris Kobach, another Republican who pushed for the legislation. The event was exactly three months after Kobach outlined tougher photo ID proposals, though the secretary of state said the bill that passed contains most of what he wanted.

“For those who are lawful citizens of Kansas, this bill will not create obstacles to casting a ballot — not at all,” Brownback said. “I think these are reasonable steps to protect the rights of our citizens. Protecting the integrity of elections is a core piece of a working democracy.”

The new photo ID requirement will take effect Jan. 1. Starting in 2013, anyone registering to vote for the first time in Kansas will have to provide proof of their U.S. citizenship, such as a birth certificate or passport, though a Kansas driver’s license could suffice for many. Also, election officials will have to verify the signatures of prospective voters before sending them a ballot by mail.

Kobach made combatting election fraud the key issue of his successful campaign last year — overcoming skepticism that it’s significant in Kansas. An intense debate over the problem’s size continues, with criminal prosecutions still rare.

The secretary of state suggested the legislation made the most significant changes in state election laws in a century.

“The biggest change before this would have been, of course, the granting of the right to vote to women,” he said. Kansas granted equal voting rights to women in 1912.

Critics contend the new law will suppress voter turnout and decrease the number of people registered to vote. They argue that poor and minority voters are most likely to be affected. Kevin Myles, president of the NAACP’s Kansas chapter, said opponents of the new law will monitor how it works.

“We are considering all options for how we could ensure that no legal American citizen is disenfranchised, as a result of administrative errors or ideological fervor,” Myles said. He did not rule out a court challenge.

Supporters strongly dispute arguments that the bill will suppress turnout or registration, or affect poor and minority Kansans disproportionately.

Kobach said the measure was written to withstand court challenges. For example, one provision requires the state to issue a free photo ID to someone who needs one for voting.

Eight other states have photo ID laws, and a statute in Oklahoma takes effect July 1, according to the National Conference of State Legislatures, though proposals have gained traction among legislators in nearly a dozen other states. Kobach said the Kansas law is stronger because it marries a photo ID provision to a proof-of-citizenship requirement and new rules for mail ballots.

“I think that really shows the rest of the country what you can do,” Kobach said. “If you want to have the top-shelf model — if you want to have the Cadillac of voter security measures — the Kansas model is the way to go.”

Legislators delayed the proof-of-citizenship rule for a year to give the state time to educate prospective voters and get a planned system for scanning citizenship documents of people seeking driver’s licenses up and running, so the documents can be provided electronically to election officials.

Myles said the delay makes the proof-of-citizenship rule more acceptable to his group, but Kobach hasn’t given up on legislators passing a follow-up bill to put the requirement in effect next year, as he proposed.

To bolster his arguments that election fraud is a serious issue in Kansas, Kobach released a study in January that said his office had received 59 reports of alleged irregularities involving at least 221 ballots since 1997.

Some allegations were based on vague reports of potential wrongdoing; most hadn’t been thoroughly investigated, and relatively few were pursued by prosecutors. Critics contend many perceived irregularities boil down to mistakes by prospective voters and even election officials themselves, not deliberate fraud.

“To say the response to that should be a radical restructuring of the entire voting system is ridiculous,” Myles said.

Myles added that even in a handful of cases where non-U.S. citizens were alleged to have cast ballots, the allegations don’t suggest they tried to impersonate someone else.

“How is the solution — how is it remotely tied to the problems?” he said.

But Kobach said the changes will discourage attempts at fraud. He said the number of past allegations are significant because local and some legislative elections are decided by a few votes.

“There’s no reason we should have any voter fraud in the state at all,” he said.